1. Field of the Invention
The present invention relates to a method and apparatus suitable for inspecting lightness of the surface of a meter dial panel, an LSI wafer or the like.
2. Discussion of the Prior Art
In a conventional lightness inspection apparatus of this kind, a television camera is arranged to take an image of a surface portion of the meter dial panel under appropriate illumination. Lightness of the taken image is compared with lightness of a reference image of the surface portion of the meter dial panel to inspect condition of the surface portion on a basis of lightness difference between the taken and reference images.
In such a construction, it is in general observed that the lightness difference described above changes relatively due to fluctuation in brightness of the illumination or imbalance in surface condition of the meter dial panel. This causes lightness difference between the taken and reference images in case that the lightness difference is to be inspected as identity. As a result, it is required to correct changes of the lightness difference. However, in case there are plural image portions to be corrected in a single taken image, it is necessary to calculate correcting amount of lightness difference on each image portion in sequence, to form a plurality of corrected taken images on a basis of the single taken image in accordance with each correcting amount of the lightness difference and also to inspect condition of lightness in relation to comparison with the respective corrected taken images with the reference image. This means that for inspection of lightness on the surface portion, complicate image processing is required to induce lowering in processing speed for inspecting lightness on the surface portion, and rising in production cost caused by increase of a memory capacity.